The present invention pertains to ice handling systems and more particularly to systems where the removal of dangers presented by icebergs to marine platforms or marine vessels located on the open seas is important.
Presently, icebergs present a constant danger to not only vessels on high seas but also offshore oil rigs or platforms located as far as several hundred miles from the coast.
Icebergs come from glaciers which end at the seashore. A glacier is a moving mass of ice that travels across the land and terminates at the ocean. As the glacier moves to the ocean, portions break off and are termed icebergs. Icebergs are primarily fresh water ice since they are composed of packed ice and snow which has been compressed over hundreds of years. The compression of snow over a large period of time results in a cohesive structure which has small bubbles or pockets of air trapped within.
Icebergs are irregular in shape, each being unique. As an iceberg travels through the ocean, it is constantly melting, at various rates dependent on the temperature of the air and water surrounding the iceberg. As such, the center of gravity will slowly change and the iceberg may roll in the water, presenting further dangers to personnel and equipment working near the iceberg.
Although icebergs are commonly encountered in the North Atlantic from the glaciers in Greenland and Canada, icebergs in smaller quantities are encountered in the Pacific from the Alaskan glaciers. Additionally, large masses of ice are encountered in the Southern Hemisphere from the Coast of Antarctica. These ice masses are similar to the icebergs located in the Northern Hemisphere, although they have a larger surface area and lower height above the water line. Many icebergs will melt at sea and never present a problem; however, many travel towards the equator along the coast line of one of the continents. These icebergs cause dangers to ships when they travel in a shipping lane or to offshore platforms, such as oil rigs, when they travel along the coast.
The danger posed to offshore platforms was not a major concern when the world oil supply was plentiful on land. However, since oil production has moved offshore, particularly in places such as the North Sea or the Hybernia Oil Field off the Coast of Newfoundland, the danger of icebergs has become a significant problem in oil production. An iceberg may weigh as much as a hundred million tons and have a water speed of one-half knot. The force with which an iceberg may collide with a platform is devastating.
Under normal conditions, an iceberg watch is kept to monitor iceberg movement. Icebergs which are within one hundred miles of a platform are checked daily to determine whether they pose a danger to a production platform. If the iceberg approaches the platform, a tow line is placed around the iceberg and an attempt is made to maneuver the iceberg to avoid collision with the platform. If the threat of collision cannot be safely avoided, a floating platform may be disconnected from the subsea wellheads and moved out of the path of the iceberg. The disconnection of a production platform may require a loss of a week's production time. Since the disconnection may require as much as 48 hours, a wide safety margin must be left to assure the prevention of a collision.
The disconnection of a production platform does not remove all detrimental effects of icebergs since flowlines are connected between an onshore storage area and the offshore production platform. Icebergs, because of their specific gravity, float with their majority of their mass beneath the surface of the water. As such, their draft or depth below the water line may be several hundred feet. Flowlines may be in only several hundred feet of water and can be damaged or severed by icebergs dragging bottom.
To reduce the draft of an iceberg, many methods have been attempted, such as blasting the iceberg apart. This method has proven unsatisfactory due to the nature of an iceberg. An iceberg is similar to a very densely packed snowball with a great amount of air trapped and compressed within as small air bubbles or pockets of air. The force of an explosive charge is absorbed by the generally deformable structure of the ice.
The method of moving icebergs by placing a tow rope around the peripheral at water level has several disadvantages. First, an iceberg is extremely unstable as it floats in the water and may roll or tip over when towing proceeds. Second, an iceberg generally decreases in size with respect to height out of the water and the tow rope may slide up and over the top of the iceberg.
Other ice masses have similar difficulties in movement by tow ropes circling the ice mass. First, the overall size of the surface area may render the length of the tow line prohibitive. Second, an ice mass having a flat surface and a low height above water may not allow the tow rope to securely rest around the ice mass.
Monitoring icebergs by aircraft iceberg watch has several deficiencies. Aircraft watch or marine vessel watch is weather related. Inclement weather or fog may inhibit aircraft availability. Either inclement weather or fog renders iceberg watch by marine vessel extremely dangerous. As a result, an iceberg may travel for several days while monitoring is impossible. If the iceberg has approached an offshore platform during the inclement weather, conditions may render the detachment and movement of the platform extremely dangerous if not impossible.